High-rate biodegradation of pentachlorophenol by biofilm developed in the immobilized soil bioreactor

A novel type of bioreactor, the immobilized soil biofilm reactor, was used for the biodegradation of pentachlorophenol (PCP) in aqueous solutions. An extremely high volumetric PCP degradation rate was obtained-up to 950 mg of PCP L-1 h(-1). The study of the biofilm growth kinetics showed that biofilm mass reached 4 g dry weight/L of reactor volume, which is much higher than values generally reported in the literature. The corresponding yield coefficient was found to be 0.054 g of biomass/g of PCP. The biofilm thickness during the PCP degradation constant rate period was below 100 mu m. A mathematical model based on a diffusion-reaction mechanism in a cylindrical shell biofilm showed that under these conditions the process is kinetically controlled. Substrate utilization kinetic data showed that the process can be described by a Monod-type model with mu(m) = 0.016 h(-1) and K-s = 5.74 mg of PCP/L. It was shown that essentially all PCP is degraded within the biofilm, with negligible liquid-phase biodegradation. The effect of different physicochemical parameters of the liquid phase on PCP biodegradation rate was also studied. The optimal temperature range was between 20 and 35 degrees C, while a 60% rate decrease was observed at 15 degrees C. The process was inhibited at pH values above 7.7, while the main water-soluble reaction product (chloride ions) affected negatively the process only at concentrations higher than 15.8 g/L. These results show that aerobic biodegradation of PCP is much less affected by variations in the different physicochemical factors when carried out in a biofilm as compared to a free suspended culture. These considerations become the bases for modeling and designing of immobilized soil bioreactors for PCP degradation in aqueous phase (such as groundwater and process water of soil washing).